The present invention relates to a gas-sealing device for a web passage section located at a wall of a treatment chamber in which a web, strip, or the like is treated by causing it to pass through a drier, a thermal treatment device, or the like.
When a web such as a plastic film is passed through a drier after being charged or a strip such as a steel strip, a copper strip or an aluminum strip is passed through a thermal treatment device, various considerations have heretofore been given to the web passage section through which the web or strip (hereinafter collectively referred to as a "web") enters or exits the drier or thermal treatment chamber in order to prevent explosion or ignition due to ingress of external air into the treatment chamber and as well as to prevent leakage of toxic gases from the treatment chamber.
In one approach, the web passage section located at the wall of the treatment chamber is provided with a nip roller for the web or a packing seal to prevent circulation of air and gases. However, a sealing device formed by a nip roller is not satisfactory in that defects on the roller can cause damage to the web, while a packing seal has the shortcoming that foreign matter adhering to the packing damages the web. To overcome these problems, non-contact type sealing devices using a gas are gaining importance.
Non-contact type gas-sealing devices for a web passage section include a suction-type gas-sealing device for continuous thermal treatment furnaces (see Japanese Patent Application Unexamined Publication No. Sho. 51-135809) and a sealing device for thermal treatment furnaces (Japanese Patent Application Unexamined Publication No. Sho. 51-136511). As shown in FIG. 4(a), the former device includes chambers 14 arranged in a continuous thermal treatment furnace. One end of the each chamber 14 communicates with the outside 2 of the furnace and the other end thereof communicates with the inside 3 of the furnace. The chamber extends vertically with respect to a web 1 that passes between the entrance and exit sections of the furnace The chamber 14 communicates also with exhaust gas passages 15, which are provided with respective gas suction devices 16.
As shown in FIG. 4(b), the latter device includes plenum chambers 17 disposed so as to confront each other interposing therebetween a moving strip 1, and nozzle sections 18 confronting both surfaces of the strip 1, arranged so as to enclose guide plates 19 on surfaces of the plenum chambers 17. To charge a gas into the plenum chambers 17 under pressure, the gas is jetted from the tapered nozzle sections 18 against the surfaces of the strip 1 so that a static pressure region 20 of the gas is formed between each plate 19 and the strip 1.
However, the sealing length L is long in both devices, which requires a large volume of gas for sealing.